Worcester Bosch Return Temperature Sensor (NTC) Fault

Boiler shows E3 and stops, usually related to return temperature sensing.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Defective return NTC sensor, Damaged sensor wiring harness, Poor connection at PCB, PCB input fault

Safety first: Turn off power before accessing internal components.

Reset once: Attempt a single reset. If E3 returns, do not continue resetting.
Visual inspection: Check the return NTC sensor connection on the return pipe inside the boiler. Look for corrosion, loose plugs, or damaged cables.
Engineer diagnosis: A professional should test the NTC resistance, inspect the harness continuity, and replace the return NTC or PCB if readings are out of range.

Medium 3/5

Return NTC Temperature Sensor

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